Method and device for purifying gases

ABSTRACT

Method for decomposing thermally decomposable components such as organic compounds which are present in gases, whereby these gases are led through a heat exchange medium consisting of particles of a substance such as clay or aluminates which resist decomposing at the decomposition temperature of the decomposable of the decomposable components, and whereby these gases are heated in the heat exchange medium up to the decomposition temperature of the decomposable components. The heat exchange medium is continuously carried around and consequently carried away from a first zone (30) in which this heat exchange medium heats the gases and is again carried to a second zone (31) in which the heat exchange medium is heated, at least partly by the waste gases of the combustion of the decomposable components and/or of the decomposition products thereof and by the remainder of the gases which were further heated by this combustion, which combustion mainly takes place in a combustion zone (32) situated between these zones (30 and 31).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application is a national stage filing under 35 U.S.C. §371 ofPCT/BE96/00004 filed 16 Jan. 1996.

The present invention concerns a method for purifying gases whichcontain thermally decomposable components, whereby these thermallydecomposable components are thermally decomposed.

2. Related Technology

By thermally decomposable components are mainly understood volatileorganic components which usually give off an unpleasant smell. Suchcomponents are for example aromatic or aliphatic compounds.

Due to the decomposition, these decomposable components are decomposedin harmless end products.

In particular, the invention concerns a method for decomposing thermallydecomposable components, in particular volatile organic components whichare present in gases, whereby these gases are led through a heatexchange medium consisting of particles which resist the decompositiontemperature, and whereby these gases are heated in said heat exchangemedium up to the decomposition temperature of the decomposablecomponents. The gases may be derived from the drying and/or burning oforganic waste and may largely consist of steam.

In a known method of the above-mentioned type, the gases are carrieddownward by means of a stationary heat exchange medium consisting ofceramic rings, in which is erected an electrical heat resistor.

In this known method, the heat exchange medium is polluted relativelyfast, so that it has to be replaced relatively quickly.

This known method cannot be used for damp gases.

BRIEF SUMMARY OF THE INVENTION

The invention aims a method for decomposing thermally decomposablecomponents which are present in gases, with an excellent heat exchange,whereby the heat exchanging mass has to be replaced less quickly andwhereby this method can also be used for damp gases.

This aim is reached according to the invention in that the heat exchangemedium is continuously carried around and consequently carried away froma first zone in which this heat exchange medium heats the gases and isagain carried towards a second zone in which the heat exchange medium isheated, at least partly by the waste gases of the combustion of thedecomposable components and/or of the decomposition products thereof andby the remainder of the gases which were further heated by thiscombustion, which combustion mainly takes place in a combustion zonesituated between these zones.

The carrying around of a heat exchange medium through which gases flowis known from U.S. Pat. No. 2,363,575, but the heat exchange medium isan adsorbent which is mainly used for drying air in a topmost zone,whereas in a bottommost zone, the adsorbent is dried by other air whichis heated by a burner. It is mentioned that the adsorbent can be acatalyst, whereby a catalytic reaction in this case takes place in thetopmost zone and whereby the catalyst is purified of adsorbed reagentsand products in the bottommost zone.

According to a particular embodiment of the invention, externalcalorific value is supplied to the combustion zone.

In the first and the second zone, the heat exchange medium is forexample moved down through due to gravitation.

The gases are preferably lead in a cross-current manner over the heatexchange medium, in such a manner that they cross said heat exchangemedium several times.

A suitable heat exchange medium is a granulated mass.

The invention also concerns a device which is particularly suitable tocarry out the method according to any of the above-describedembodiments.

Thus, the invention concerns a device for thermally decomposingthermally decomposable components which are present in gases,characterized in that it contains a tower with three coaxial cylindricalstanding casings including an inner casing provided with openings whichis closed at the bottom and at the top, a second casing provided withopenings erected around this inner casing and an outer casing whichsurrounds this second casing. Walls are provided in the space betweenthe second casing and the outer casing, which walls divide this space inchambers which are situated on top of one another and which open intothe space between the second casing and the inner casing via saidopenings in the second casing. The space inside the inner casing isdivided in a top chamber and a bottom chamber by at least one partition;the device further includes a heat exchange medium between the innercasing and the second casing which consists of particles; means tocollect this heat exchange medium at the bottom of the tower and tosupply it back to the top of the tower between the inner casing and thesecond casing; and means to introduce the gases at the bottom throughthe second casing and to discharge the gases at the top through thesecond casing, said means comprising an inlet for the gases which opensinto a chamber situated at the bottom and an exhaust for the gases whichopens into a chamber situated at the top.

Practically, the device contains means to supply calorific value fromoutside to the gases between the inlet and the exhaust, either in theshape of hot gases or in the shape of injected fuel.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better explain the characteristics of the invention, thefollowing preferred embodiment of a method and device according to theinvention for decomposing thermally decomposable components which arepresent in gases is described as an example only without beinglimitative in any way, with reference to the accompanying drawings, inwhich:

FIG. 1 schematically shows a section of a device for decomposingthermally decomposable components according to the invention;

FIG. 2 shows a section according to line II--II in FIG. 1; and FIG. 3shows the detail which is indicated by F3 in FIG. 1 to a larger scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As represented in the figures, the device for decomposing thermallydecomposable components which are present in gases 33 contains a tower 1which mainly consists of three coaxial standing casings 2, 3 and 4 whichfor cylinders which are conically tapered on both ends.

The inner casing 2 is closed at the top and at the bottom and isprovided with openings 5 in its cylindrical part.

The space inside this casing 2 is divided by partitions 6 in a topchamber 7 and a bottom chamber 8.

As represented in detail in FIG. 3, this casing 2 can be made of hollowflame-resistant stones 9 which are provided with windows 10 in theirbent walls which form the above-mentioned openings 5 together with thecavity 11 in the stones.

The second, in other words the middlemost casing 3 is also provided withopenings 12 in its cylindrical part and can be made of similarflame-resistant stones 9 in the same manner as the inner casing 2.

The outer casing 4 is a solid wall of for example gas concrete.

The conically tapered outer parts of these casings 3 and 4 are open attheir end, such that at the top and at the bottom of the tower 1, theyrespectively form an inlet 13 and an exhaust 14 which open into thespace 15 which is formed between the inner casing 2 and the secondcasing 3.

The space between the second casing 3 and the outer casing 4 is dividedby ring-shaped walls 16 in three ring-shaped chambers situated on top ofone another, namely a bottom chamber 17, a middlemost chamber 18 and atopmost chamber 19.

In case the second chamber 3 is formed of hollow stones 9 at the placeof a ring-shaped wall 16, the hollow stone 9 is replaced by a solidstone in order to prevent that the chambers 17, 18 and 19 are directlyconnected to one another via the casing 3.

The space between the inner casing 2 and the second casing 3 is notinterrupted but filled with a heat exchange medium in the shape of agranulated mass consisting of particles which resist decomposing at thetemperatures required to dissolve the volatile organic components in thegases and which in particular resist temperatures of 800° to 900° C. Forclarity's sake, this granulated mass is not represented in FIG. 3.

Suitable particles are particles which easily absorb and give off heatsuch as burnt clay, aluminate, for example calcium aluminate or acomposition containing aluminate.

Not only can these particles ensure a good heat transfer, but possiblythey can also have a catalytic action.

The gases 33, which are derived from the drying and/or burning oforganic waste, for example which are derived from a waste treatmentunit, and which mainly consist of steam with volatile, thermallydecomposable organic components which are usually harmful, can besupplied via an inlet 20 which opens into the bottom chamber 17 throughthe outer casing 4 by means of a fan 21 mounted in this inlet.

To this inlet 20 is connected a pipe 22 for supplying hot air to thegases 33.

The gases are discharged from the top chamber 19 via an exhaust 23 whichextends through the outer casing 4 and in which is also mounted a fan34.

Calorific value or heat can be supplied to the granulated mass by meansof a ring-shaped gas pipe 24 which is erected in the middlemost chamber18, which is provided with openings and is connected to an externalburner 25 which is erected outside the outer casing 4.

The outer casing 4 is further surrounded by a housing 26 through whichthe above-mentioned inlets 13 and 20 and the exhausts 14 and 23 extend.

Under the exhaust 14 for the granulated mass is erected a dischargescrew 27 and above the inlet 13 for this granulated mass is erected asupply screw 28. In order to carry the granulated mass from one screw tothe other, an elevator 29 is provided between the discharge screw 27 andthe supply screw 28.

A quantity of hot air, preferably up to 10 vol %, is added to the gasesvia the pipe 22 to supply a sufficient amount of oxygen for thecombustion of the thermally decomposable components and/or decompositionproducts thereof as well as air for the possible combustion of the gasesinjected via the gas pipe 24.

This air preferably has a temperature of over 650° C., which alsoprovides for a pre-heating of the gases 33, and, if these gases containsteam, lowers the saturation temperature of this steam and in thismanner prevents condensation.

The principle of the gas purification, or in other words thedecomposition of the decomposable components into harmless end products,consists in making the granulated mass circulate and leading the gases33 in counterflow in relation to a downward flow of this granulatedmass, whereby the gases cross the flow of the granulated mass severaltimes.

This crossing becomes possible as the inner casing 2 and the secondcasing 3 are provided with openings 5, 12 respectively.

At a normal regime, the gases 33 are heated in a first, bottommost zone30 of the granulate mass by the latter, whereas in a second, topmostzone 31 this granulated mass is heated by the waste gases of thecombustion or pyrolysis of the volatile organic components and/ordecomposition products thereof on the one hand, and by the waste gasesof the external burner 25 which are introduced in the combustion zone 32situated between the zones 30 and 31 via the gas pipe 24.

The gases 33, at a temperature between 150° and 200° C., are blown inthe bottommost zone 31 via the inlet 20 and the bottommost chamber 17and through the second casing 3.

As indicated by the arrows, the main part of these gases flows throughthe granulated mass and through the inner casing 2 in the bottommostchamber 8, whereby these gases are heated.

The gases 33 are stopped by a partition 6 and as a result again flowright through the zone 31 up to the middlemost chamber 18 between thecasings 3 and 4, whereby they are further heated by the granulated mass.

During said heating of the gases, at least a part of the decomposablecomponents usually already start to decompose into gaseous decompositionproducts which can be further thermally decomposed or burnt.

In this middlemost chamber 18 and the part of the granulated massconnected to it via openings 12 in the second casing 3 is formed thecombustion zone 32. In this combustion zone 32, the furtherdecomposition of the decomposable components and/or decompositionproducts thereof takes place, and especially the combustion of thegaseous decomposition products into harmless end products, in particularCO₂, H₂ and N₂. In this combustion zone 32, also the waste gases of theexternal burner 25 are possibly further burnt.

The temperature of the gases rises in this combustion zone 32 with over100° C., up to 800° to 900° C. or even more.

According to a variant, either ordinary heated gases or pure, forexample gaseous fuel can be supplied via the gas pipe 24 instead ofwaste gases.

Due to the injection of gases via the gas pipe 24 in the combustion zone32, an excess pressure of less than 1.05 times the atmospheric pressureis created, and these gases are spread in the other gases. Thus, theformation of nitrogen oxides is prevented.

On top of the middlemost chamber 18, the hot gases again radially flowthrough the granulated mass, namely the topmost zone 31 thereof, intothe chamber 7, whereby the gases heat the granulated mass.

Thanks to the fan 34 in the exhaust 23 for the gases and because thechamber 7 is closed at the top, the predominantly purified gases flow,opposite the exhaust 23, radially outward from the chamber 7 through thegranulated mass, such that they further heat this granulated mass.

These gases are discharged via the topmost chamber 19 and the exhaust 23and leave the tower 1 at a temperature of over 150° C.

During this circulation of the gases 33, the granulated mass is carriedaround. This mass continuously descends in the space 15 between theinner casing 2 and the second casing 3 due to gravitation.

At the bottom, cooled granulated mass is collected on the dischargescrew 27. This mass is carried via the elevator 29 on the supply screw28 and carried to the top of the space 15 by this supply screw.

The heat exchange between the granulated mass and the gases is excellentand the purification of the gases by means of decomposition orcombustion of the thermally decomposable components can be carried outin a very economic manner.

Although the granulated mass is self-cleaning to a large extent, it canbe further cleaned outside the tower 1 during the circulation. Duringthe purification, this granulated mass can be replaced in part or as awhole by new mass.

In the tower 1, the granulated mass can operate as a filter which stopsthe solid particles which may possibly be present in the gas flow, whichpreferably flows at a speed which is lower than 1.5 m/sec. During thecleaning of the granulated mass, these solid particles can then beremoved via the discharge screw 27.

Components such as metals which have been released during thepurification, in particular copper, can precipitate on the particles ofthe granulated mass when it cools off. Thanks to the mutual friction ofthe particles as the granulated mass moves, this precipitation of theparticles is removed.

The method can be applied to damp gases, but these gases must notnecessarily consist mainly of steam.

The circulation of the granulated mass must not necessarily take placeby means of an elevator. It can for example also take place by means ofscrews or such.

Also the flow of the gases must not necessarily be caused by means oftwo fans. It can also be done with a single fan or with one or moreextractors.

Calorific value from outside the combustion zone is added as required.It is not excluded that, once the starting up is over, such addition isno longer required as the decomposition or combustion of the organiccomponents in the gases provides sufficient heat to keep thedecomposition going.

The present invention is by no means limited to the above-describedembodiments represented in the accompanying drawings; on the contrary,such a method and device can be made in all sorts of variants whilestill remaining within the scope of the invention as described in thefollowing claims.

I claim:
 1. A method of decomposing thermally decomposable componentswhich are present in gases, comprising the steps of:a) passing gasescontaining thermally decomposable components through a heated, flowableheat exchange medium comprising heated particles which resistdecomposing at the decomposition temperature and heating said gases bythe heated heat exchange medium at least up to the decompositiontemperature of the decomposable components; b) continuously circulatingthe heated heat exchange medium to a first zone in which the heatexchange medium heats the gases and to a second zone in which the heatexchange medium is at least partly heated by the waste gases of acombustion of the decomposable components and/or of the decompositionproducts thereof and by the remainder of the gases which were furtherheated by this combustion, said combustion being carried outsubstantially in a combustion zone situated between the first and secondzones.
 2. The method according to claim 1, wherein the thermallydecomposable components in the gases are volatile organic components andthe gases in the combustion zone are heated up to 800° C. or more. 3.The method according to claim 1, wherein before the gases reach thecombustion zone, air is supplied to the gases.
 4. The method accordingto claim 3, including supplying the air at a temperature of over 650° C.5. The method according to claim 3 wherein up to 10% by volume of air isadded to the gases.
 6. The method according to claim 1, including addingcalorific value other than combustion of said gases to the combustionzone.
 7. The method according to claim 1 including providing an excesspressure in the combustion zone of less than 1.05 times the atmosphericpressure.
 8. The method according to claim 1 including moving the heatexchange medium in the first and second zones by gravity, and passingthe gases in a cross-current manner through the falling heat exchangemedium, such that the gases cross said heat exchange medium severaltimes.
 9. The method according to claim 1 including using a granulatedmass as the heat exchange medium.
 10. The method according to claim 9,including using as the granulated mass a material selected from thegroup consisting of clay, aluminate and a composition containingaluminate.
 11. A device for thermally decomposing thermally decomposablecomponents which are present in gases, comprising; a tower having threecoaxial cylindrical standing casings, including a first inner casingprovided with openings and which is closed at the bottom and at the top;a second casing provided with openings erected around the inner casing;and a third outer casing which surrounds the second casing; transversedivider walls disposed in the space between the second casing and thethird casing, said divider walls dividing the said space into verticallyspaced outer chambers which open into the portion of the space betweenthe second casing and the first casing via said openings in the secondcasing; the volume inside the inner casing being divided into a topinner chamber and a bottom inner chamber by at least one innertransverse partition; a heat exchange medium contained between the firstcasing and the second casing, said medium comprising heated particles;means to collect the heat exchange medium at the bottom of the tower andto circulate it back to the top of the tower between the inner casingand the second casing; and means for introducing gases containingthermally decomposable components at the bottom of the tower into thesecond casing and to discharge the gases out of the top area of thesecond casing, said means comprising an inlet for the gases which opensinto an inlet chamber situated at the bottom of the tower and an exhaustfor the gases which opens into an exhaust chamber located at the top ofthe tower.
 12. The device according to claim 11, including means tosupply calorific value from outside of the tower to the gases betweenthe inlet and the exhaust for the gases.
 13. The device according toclaim 12, wherein said vertically spaced outer chambers include at leasta middlemost outer chamber, and wherein said means to add calorificvalue to the gases includes a gas supply pipe which discharges into saidmiddlemost outer chamber.
 14. The device according to claim 13, whereinsaid means to add calorific value to the gases includes an externalburner outside the outer casing.